In the transmission of a signal with varying frequency, each frequency will travel through a cable at a different rate. For the cable used in audio products the frequency generally ranges from 20 Hz to 20 KHz. This represents a 1000:1 ratio of the frequency being conducted through a cable. For higher frequency signals such as used in RF feed lines the signal the frequency being conducted ranges as high as several hundred megahertz. Because of the variation of frequencies being transmitted the materials and construction of cables for each application would be different. For audio cables the frequency components of the signal are launched synchronized in time but they emerge with the low frequencies delayed more than the high frequencies, resulting in group delay time smear. The frequency group delay time smear must be minimized in order to maintain the integrity of the signal being passed from one device to another to reproduce the best quality audio sound, for example a high fidelity audio reproduction, and likewise in video signal reproduction or data transmission.
Cables used in the transmission of high fidelity signals are used to interconnect audio components as well as to connect audio amplifiers to loudspeakers. While interconnect cables and loudspeaker cables both transmit the audio frequency range of 20 Hz to 20 KHz, the construction of interconnect cables and loudspeaker cables is significantly different. As a simple example, the cables connecting audio components can be highly resistive, with the cables used between the amplifier and the speakers must be highly conductive. In a further example, the cable connecting audio components are generally short in length, while the cables connected from the amplifier to the speakers is frequently much longer in length. Prior art high fidelity music signal cables inherently corrupt to one degree or another, complex waveforms during their travel from source to load. The human ear is keenly sensitive to time smearing signals, which detract from the illusion of a live musical performance as appreciated by the listener.
Inductive Reactance
Inductive Reactance is found using the Kirchhoff's loop rule that dictates that the magnitude of the potential difference across the inductor must equal the electro motive force (emf) of the generator. Generally the maximum potential difference equals the maximum current times the inductive reactance. This relationship is described with the equation XL=ωL, where XL is the inductive reactance, ω is the angular frequency of alternating current and L is the inductance. The greater the inductive reactance the less the maximum current. A conductor with greater inductance provides more opposition to the flow of current through the conductor, which reduces the maximum flow if the alternating current in the circuit so the faster the change (higher frequency) the more the inductor opposes the frequency. Inductance can be affected by several factors. For example, the size of the wire where the larger the diameter of the wire, the larger the inductance. Moreover, the lower the electrical resistance of a conductor, hence with greater current-carrying ability, the greater the inductance.
Skin Effect
Skin effect occurs in conductive materials when AC is applied. Skin effect forces electrons to flow from a maximum occupation of one-half the conductor's diameter or thickness cross-section to an ever-diminishing fraction of that diameter or thickness as electrons migrate nearer to the surface of the conductor and increasing the resistance to the flow of current. Skin effect forces the lower frequencies of the signal to travel in a restricted manner and delay the transmission of those frequencies. Higher frequencies will separate and travel faster through the conductor and reach the load before the lower frequencies.
There are currently numerous electrical cables available that attempt to minimize deleterious frequency-sensitive group delay time-smear artifacts. Seen among these products is a preponderance of cables using, for example, highly conductive high purity silver or copper conductors, and embracing a multitude of geometric constructions designed to counteract or minimize inductive reactance. Cables are also fabricated using various types of shielding to minimize noise, and certain cables use passive network elements added to the cable in attempts to minimize frequency sensitive group delay time smear. It is important to note that skin depth in a highly resistive alloy, such as nichrome, is approximately thirty times deeper than the skin depth of highly conductive metals such as silver or copper.
Skin Effect in Resistive Materials
The current related art has focused on reducing the inductance of audio, video and data interconnect cables by using a variety of geometries, as well as highly conductive metals such as copper and silver in an attempt to minimize frequency sensitive group delay time smear. Such cables may still produce frequency delays up to tens of milliseconds that cause, in the case of audio reproduction, signals to separate into distinct sounds that when emitted from the loudspeaker are audible to the listener. Further disadvantageously, the ability of such cables to minimize frequency sensitive group delay time smear is dependent upon numerous external factors, such as spacing of the source and return wires, dielectric media, the type of and disposition of shielding, the braiding geometry and the gauge of the wire used in the cable. These factors increase the cost and complexity of the cables without significantly reducing group delay time smear.
Conductors that are made with different material exhibit different conductive, resistive and inductive characteristics. The resistance of conductors is shown as σ and is described in ohms per meter Copper has a σ of 58×106 mhos/m, Aluminum has a σ of 37×106 mhos/m, silver has a σ of 61×106 mhos/m, gold has a σ of 45×106 mhos/m, Tin has a σ of 7.5×106 mhos/m, Lead has a σ of 4.1×106 mhos/m, Nickel with 18% silver has a σ of 3.1×106 mhos/m, Nichrome has a σ of 0.015×106 mhos/m, 304 stainless steel has a σ of 4.2×106 mhos/m.
Resistive Swamping
Resistive swamping is a method to keep an electrical frequency response curve flat and prevent signal overcompensation across a narrow range of frequencies. The use of resistive swamping circuit to overcome inductive reactance is widely used in electrical circuit design, by paralleling an inductor, i.e. bridging, with a resistor. Heretofore the use of an inherently resistive conductor to nullify the selfsame conductors' inductive reactance to the same effect has not been employed in signal transmission cables. The swamping of inductance by the implementation of resistance conductors forces the cable to assume a posture of a fundamental resistance potential divider, where electrical resistance overcomes inductance, and is therefore free of group delay time-smear otherwise caused by inductive reactance. When a cable comprised of resistance conductors is employed, for example, in an audio interconnect circuit, the resistance of the cable will reduce the audio gain level by a minimally small amount. With the addition of a minimal amount of audio gain by slightly turning up the gain of the volume control, the signal gain level will be restored to the gain level of a typical prior art cable that are typically comprised of highly conductive metals such as copper or silver. However, with the present novel new cable, the group delay time smear caused by inductive reactance will now be suppressed beneath the normal noise floor of the audio signal. Hence the group delay time smear associated with inductive reactance will now be removed from the audible signal, or, put another way, the deleterious group delay time smear will now be left well below the audible signal.
Capacitive Reactance
Capacitive reactance is the opposition to the passage of alternating (AC) current in electrical components or wires that is caused by the capacitance coupling that exists between to conductors that are carrying opposing or different signals. The relationship is described with the equation Xc=1/(2πfc), where f is the AC frequency in hertz and c is the capacitance in farads. The reactance Xc is large at low frequencies and small at high frequencies. For steady direct current (DC) the capacitive reactance is infinite.
Proximity Effect
The Proximity Effect explains the effect of two conductors running adjacent to each other where the signal from one conductor affects the signal in the other conductor based upon the proximity of one conductor to another conductor, or a group of conductors. The proximity effect is also called current-bunching, in that a predominance of current in adjacent conductors is greatest, that is, bunches, in the cross-sectional area of the conductors where the forward signal-carrying conductor and the return signal-carrying conductor are in closest proximity to one another. If it is desirous to force audio or video currents to travel within a preferred domain within the body of a conductor, the phenomenon may be accomplished by disposing the preferred domain of the metallic conductors in close proximity to one another and therefore take advantage of the proximity effect. Due to the proximity effect, audio signals that exist in the cable that pass closest to each other in parallel audio signal cable, i.e. the higher frequencies, will be affected the greatest, dependent upon frequency, and in keeping with the dictates of the skin effect, while signals less affected by skin effect, i.e. the lower frequencies, that exist in the core and/or the sides of the conductors opposite the proximate sides of the conductor, will be less affected by the proximity effect. The optimum implementation of the proximity effect is seen in the present invention in the employment of ribbon conductors. Contiguously disposed ribbon conductors will benefit from both the skin effect, and the proximity effect, in embodiments where the predominant currents will flow on or near the surfaces of the facing sides of the ribbons so contiguously disposed.
The best threshold of the audibility of frequency group time delay have been provided by Blauert, J. and Laws, P “Group Delay Distortions in Electroacoustical Systems”, Journal of the Acoustical Society of America, Volume 63, Number 5, pp. 1478-1483 (May 1978) and are shown in the table below.
FrequencyThresholdPeriodCycles8kHz2ms0.125ms164kHz1.5ms0.25ms62kHz1ms0.5ms21kHz2ms1ms2500Hz3.2ms2ms1.6The Group Delay is equal to −(Δ φ)/(Δ ω) where φ is the phase angle and ω is the frequency. Exceeding these values degrades and distorts the transmitted analog or digital signals producing data error or audible miscues. The period of a 2 KHz signal is 0.5 ms and therefore a 2 KHz signal being delayed 1 ms would be delayed two complete cycles.
Presently available cables designed to connect audio, video and data devices together inherently corrupt the complex analog waveforms or the bit stream during the signal's travel from source to load causing distorted analog signals and potential detrimental reduction of data bit rates because of inductive reactance and/or the skin effect. Both inductive reactance and skin effect impose the group time delay effect upon signals in a frequency-dependent manner.
Therefore there exists a need for an electrical cable that minimizes frequency-sensitive group time delay in audio, video and data communications interconnect cables that does not embrace these disadvantageous properties.